The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Frequency responses of electronic circuits are tuned in various applications, such as wired or wireless switches, controllers, transceivers, filters, power management units, data storage units, etc. Current techniques used to tune a frequency response have limited resolution and limited noise minimization control.
In addition, some tuning circuits tend to require additional terminals and system board space. For example, tuning circuits with crystal oscillators are used for high accuracy and low temperature drift tuning applications. A crystal oscillator, when used as a separate stand-alone device, is coupled to one or more pins of an integrated circuit and consumes system board space.
To save system board space, varactor diodes may be used and included in an integrated circuit. However, when capacitance of a varactor diode is tuned, such as by applying an analog control voltage in an open loop manner, noise problems result. Although current of the integrated circuit can be increased in order to reduce the noise, increased current results in increased power consumption. Increased power consumption decreases the working life of battery powered electronic systems.
Digitally adjusted capacitors, such as capacitors that are connected or disconnected using a switch, can be used to reduce noise in a tuning circuit. Digitally adjusted capacitors are typically either equally or binarily weighted. When equally weighted, a large number of capacitors and corresponding switches provide tuning with a large tuning range and a fine resolution. Where binarily weighted, capacitors with small capacitance values are limited in size by parasitic capacitances of the switches. Capacitors with large capacitance values are limited by available die area.